1. Field of the Invention
The invention relates to an improved process for making a mild, detergent-soap, toilet bar containing, by weight, about 45% to 70% of sodium or potassium C6-C18 acyl isethionate, about 10% to 40% of C12-C20 fatty acids as a plasticizer and superfatting agent, about 3% to 25% of a water-soluble sodium or potassium soap and 2% to 10% of water which comprises the step of forming a liquid mixture of said isethionate, said fatty acids and said soap in the presence of from 0.5% to 2.5% by weight based upon the toilet bar of a vegetable oil at a temperature of from about 85.degree. C. to 105.degree. C. The liquid mixture formed in the presence of the vegetable oil has a reduced viscosity as compared with an identical mixture made without said vegetable oil and yields bars with improved slip, low isethionate degradation and low grit.
2. Description of the Prior Art
Mild, detergent-soap, toilet bars containing C6-C18 acyl isethionate as the principal detergent and minor amounts of fatty acids and soap are disclosed in U.S. Pat. No. 2,894,912 (Geitz) and U.S. Pat. No. 3,376,229 (Haass et al.). In Geitz, the chips processed into bars were produced from either a 40-50% aqueous slurry of the ingredients mixed at a temperature of from 38.degree. C. to 93.degree. C. or a mixture of the dry ingredients mixed at 100.degree. C. for a long period of time. In Haass et al., the bars were prepared from a liquid mixture of acyl isethionate, fatty acids, anionic syudet and soap mixed at a temperature of about 110.degree. C. to 113.degree. C. for about fifteen minutes. The latter bars contained at least about 4% by weight of sodium isethionate as a processing aid.
In U.S. Pat. No. 4,707,288, mixtures of acyl isethionate, fatty acids, soap and more than 2% by weight of sodium isethionate were mixed in particulate form at temperatures in the range of 60.degree. C. to 86.degree. C. using a special cavity transfer mixer under conditions of high shear to yield toilet bars which exhibit reduced grit.
U.S. Pat. No. 4,696,767 discloses a process for making mild toilet bars wherein a slurry of acyl isethionate, water and a polyol such as sorbitol is formed into a stable solution by heating at a temperature of from 100.degree. C. to 120.degree. C. at 4-10 p.s.i.g. and said slurry is mixed with neat soap and this mixture is heated to about 150.degree. C. under a pressure of 4 atmospheres before being spread on a chill roll to provide flakes which yield a toilet bar without grit. However, the presence of the polyol leads to increased water penetration in the soap dish as well as a bar of increased cost. This patent further teaches that use of acyl isethionate in particulate form causes problems--fine particles function as a lacrimatory agent and larger particles yield bars with grit.
In U.S. Pat. No. 4,663,070 a toilet bar composition in which soap is the principal surfactant is described. Liquid mixtures containing a major proportion of soap plus acyl isethionate, fatty acids, water and sodium isethionate were formed at temperatures of 96.degree. C. to 103.degree. C. In U.S. Pat. No. 5,030,376 a similar mixture containing a major proportion of soap is processed under conditions of high shear in a special cavity transfer mixer at temperatures maintained below 40.degree. C. to form a mixture with some of the soap in the delta phase. U.S. Pat. No. 5,041,233 also relates to a similar mixture wherein a mixture of acyl isethionate, fatty acids and soap is prepared at a temperature of 82.degree. C. to 94.degree. C., with the soap being formed in situ. This patent indicates that high viscosity mixtures and hydrolysis of acyl isethionate can be problems in such mixtures.
The foregoing description of the prior art indicates that a variety of processes have been employed to produce mild, detergent-soap, toilet bars which have satisfactory hardness, water permeability, slip and low grit. Additionally, the resultant bars should exhibit low hydrolysis of the sodium isethionate. Also, desirably, the process should utilize standard equipment and should not require process temperatures higher than about 110.degree. C. to avoid degradation of acyl isethionate and to conserve energy.